# MtrXTools > Free network diagnostics: DNS, SSL/TLS, HTTP headers, SPF/DKIM/DMARC, RDAP/WHOIS, IP and cloud ownership, ports, ping and NTP, plus an explainer for about 280 common error messages. No account needed; results are not stored. Every check runs live against the target, so results reflect the current state of a domain or server. Tool pages accept the input in the URL, e.g. https://www.mtrxtools.com/dns-lookup?q=example.com&type=MX, and the same checks are available as a free JSON API. ## Tools - [DNS lookup](https://www.mtrxtools.com/dns-lookup): Look up A, AAAA, MX, TXT, NS, SOA, CAA and DNSSEC records from Cloudflare, Google, Quad9 or the authoritative servers, with TTLs and flags. Free. - [Reverse DNS](https://www.mtrxtools.com/reverse-dns): Find the hostname behind an IPv4 or IPv6 address (PTR record) and check that it resolves back to the same IP: forward-confirmed reverse DNS. Free. - [SSL/TLS checker](https://www.mtrxtools.com/ssl-checker): Check a site's SSL/TLS certificate: expiry, hostname match, chain of trust, key strength and TLS 1.0 to 1.3 support, graded A+ to F with fixes. - [HTTP headers](https://www.mtrxtools.com/http-headers): See every redirect and the raw HTTP response headers for any URL, and grade security headers: HSTS, CSP, X-Frame-Options, Referrer-Policy and more. - [Website health](https://www.mtrxtools.com/website-health): A graded website health report: DNS, every server IP tested on its own, http/https and www redirects, TLS renewal risk, HSTS and domain expiry. - [Expiry calendar](https://www.mtrxtools.com/expiry-calendar): Calendar reminders before SSL certificates, domains and security.txt expire. Subscribe in Google Calendar, Outlook or Apple Calendar. - [Status badges](https://www.mtrxtools.com/status-badges): Free SVG badges for READMEs and status pages: certificate expiry, TLS grade, security headers grade and DMARC policy, updated automatically. - [SPF, DKIM & DMARC](https://www.mtrxtools.com/email-auth): Check a domain's SPF record and lookup count, find DKIM keys, read the DMARC policy, and see MTA-STS, TLS-RPT and BIMI, with a grade and fixes. - [Email header analyser](https://www.mtrxtools.com/email-headers): Paste raw email headers to see each hop and its delay, SPF, DKIM and DMARC results and spoofing red flags. Runs in your browser, never uploaded. - [DMARC report analyser](https://www.mtrxtools.com/dmarc-reports): Upload DMARC aggregate reports (.xml, .gz, .zip) to see who sends as your domain, which senders fail SPF or DKIM, and when to move to p=reject. - [RDAP lookup](https://www.mtrxtools.com/rdap): Look up domain, IP range or ASN registration data over RDAP, the modern WHOIS: registrar, dates, status, nameservers and abuse contacts. - [WHOIS](https://www.mtrxtools.com/whois): Query WHOIS servers directly for any domain or IP, following referrals from IANA to the registry and registrar, and see every raw response. Free. - [IP info](https://www.mtrxtools.com/ip-info): Look up any IP address or hostname: approximate location, network owner and ASN, address type (public, private, CGNAT) and reverse DNS. Free. - [Cloud IP owner](https://www.mtrxtools.com/cloud-ip): Is this IP AWS, Azure, Google Cloud, Cloudflare, Fastly, Oracle or DigitalOcean? See the service and region, and verify Googlebot or Bingbot. - [What's my IP](https://www.mtrxtools.com/my-ip): See your public IPv4 and IPv6 address, your network provider and approximate location as websites see them. Free, instant, no sign-up. - [Ping (TCP)](https://www.mtrxtools.com/ping): Measure latency to any host by timing TCP handshakes on port 443 or any port: min, average, max, jitter and loss. Works where ICMP ping is blocked. - [Port check](https://www.mtrxtools.com/port-check): Check if TCP ports are open, closed or filtered on any host, with presets for web, mail, remote access and databases, connect times and banners. - [NTP test](https://www.mtrxtools.com/ntp-test): Query an NTP time server over UDP 123 and see its clock offset, round-trip delay, stratum, reference source, leap status and root distance. Free. - [Subnet calculator](https://www.mtrxtools.com/subnet-calculator): Calculate network and broadcast addresses, usable host range, netmask and subnet splits for any IPv4 or IPv6 CIDR block. Runs in your browser. - [Network planner](https://www.mtrxtools.com/network-planner): Summarise CIDR blocks into the fewest prefixes, find the range holding an IP, convert netmasks to wildcard masks with ACL snippets, plan IPv6. - [Error explainer](https://www.mtrxtools.com/error-explainer): Paste an error from a browser, curl, Python, Java, Go, git, SSH, Docker, nginx, Cloudflare or an email bounce: see what it means and how to fix it. ## API Free, keyless JSON API. GET with query parameters; responses are {"ok": true, "ms": ..., "data": {...}} or {"ok": false, "error": "..."}. Rate limited per IP. - [API documentation](https://www.mtrxtools.com/developers) - [OpenAPI 3.1 description](https://www.mtrxtools.com/api/v1/openapi.json) - [DNS lookup](https://www.mtrxtools.com/api/v1/dns-lookup): Query DNS records from a public resolver or straight from the domain's authoritative nameservers, with TTLs and flags. - [Reverse DNS](https://www.mtrxtools.com/api/v1/reverse-dns): Find the PTR hostname for an IPv4 or IPv6 address and check that it resolves back to the same address. - [SSL/TLS checker](https://www.mtrxtools.com/api/v1/ssl-checker): Read the certificate chain a server sends, check expiry, hostname match, trust and key, test TLS 1.0 to 1.3, and grade it. - [HTTP headers](https://www.mtrxtools.com/api/v1/http-headers): Follow every redirect, return each hop's status, headers and timing, and grade the security headers of the final page. - [Website health](https://www.mtrxtools.com/api/v1/website-health): A graded site report: DNS, every A/AAAA address, the http/https and www/apex redirect matrix, TLS, accepted cipher suites, headers, domain expiry and content basics. - [SPF, DKIM & DMARC](https://www.mtrxtools.com/api/v1/email-auth): Check SPF (with the DNS lookup count), find DKIM keys, read the DMARC policy, MTA-STS, TLS-RPT and BIMI, and grade the setup. - [RDAP lookup](https://www.mtrxtools.com/api/v1/rdap): Registration data over RDAP: registrar, dates, status, nameservers and abuse contacts for a domain, IP address or range, or AS number. - [WHOIS](https://www.mtrxtools.com/api/v1/whois): Query WHOIS servers directly, following referrals from IANA to the registry and registrar, and return each raw response. - [IP info](https://www.mtrxtools.com/api/v1/ip-info): Network, AS number, approximate location, address type and reverse DNS for an IP address. Hostnames are resolved first. - [Cloud IP owner](https://www.mtrxtools.com/api/v1/cloud-ip): Which cloud, CDN or crawler owns an address, from each provider's published ranges, with service and region. Verifies Googlebot and Bingbot. - [What's my IP](https://www.mtrxtools.com/api/v1/my-ip): The public IP address the request came from, with its network and approximate location. - [Port check](https://www.mtrxtools.com/api/v1/port-check): Whether TCP ports are open, closed or filtered, with connect times and the banner a service sends first. Up to 20 ports. - [Ping (TCP)](https://www.mtrxtools.com/api/v1/ping): Round-trip time to a host from timed TCP handshakes: min, average, max, jitter and loss. Works where ICMP is blocked. - [NTP test](https://www.mtrxtools.com/api/v1/ntp-test): Query an NTP server over UDP 123: clock offset, delay, stratum, reference, leap status and root distance, over several samples. - [Error explainer](https://www.mtrxtools.com/api/v1/explain-error): Match an error message or log line against MtrXTools's error library: what it means, causes, fixes, and the check that confirms it. ## Errors - [Error explainer](https://www.mtrxtools.com/error-explainer): paste an error message to get its meaning, causes, fixes and the check that confirms it. Each known error also has a page at https://www.mtrxtools.com/errors/.